Last updated: 22 April 2004

Focus Shaft Fix

From: Kevin Sterling (kevin_sterling@bigfoot.com)

Please Note: This article assumes you have basic mechanical skills and tools. Performing this work will probably void your warranty; proceed at your own risk!

Focus Shaft Fix

(click on any image for a larger picture)

First you will need to remove the optical tube from the fork arms.


1.      Remove the four hex screws (two on each side) at the rear of the optical tube.

2.      Gently spread the forks so as to remove the optical tube

optical tube removal_640_480.jpg (39768 bytes)

3. Remove the three (two) hex screws from the rear so you can slide off the plastic cover.

cover removal_640_480.jpg (42494 bytes)

4. Mark a line on the mirror block and aluminum tube so you can register the mirror block back into the housing. If you don't do this collimation might be affected, on mine registeration was hand tight.

wpe5.jpg (7965 bytes)

5. Unscrew the focus mirror block from the optical tube, be gentle and DO NOT TOUCH THE PRIMARY MIRROR SURFACE

6. Replace the focus  shaft into the mirror block

focuser_800_600.jpg (86459 bytes)

Subject:	Re: Focuser knob damage to ETX 90
Sent:	Thursday, April 22, 2004 00:36:04
From:	"P. Clay Sherrod" (drclay@tcworks.net)
Several ways of attacking this and really none are good for the
inexperienced; the blue tube will unscrew from the rear cell; grab the
black rear cell tightly with one hand and carefully begin to unscrew the
barrel with the other; once off you will be able to see the mirror and
mirror sled/baffle tube; if you can gently pull on the mirror you might
be able to access the clip and pin for the focus rod and reattach; if
not, then you must remove the entire OTA assembly FROM the rear cell via
the three recessed screws you will see deep inside the very back of the
tube in the black cell....take those out and the entire OTA assembly
will come out; you must first remove the focus knob.  Once off, you will
again need to unscrew the blue tube to gain access to the focus rod....
Not an easy job.  Best of luck.

Dr. P. Clay Sherrod
Arkansas Sky Observatory
Harvard MPC H41 (Petit Jean Mountain)
Harvard MPC H43 (Conway)
Harvard MPC H44 (Cascade Mt.)

----- Original Message ----- 
	From: Keith
	Hi Clay,
	I ran into a problem with my focuser knob on my ETX 90 EC that seems
	similar to what you describe on Mike Weasner's web site. It started when
	I bought a Shutan ETX wide-field diagonal. I found it was right at the
	limit of my focuser with my Antares eyepieces, and in trying to get it
	to reach focus I'm afraid that I forced it and damaged the focus
	apparatus -- it started to turn freely as if it was disconnected. I have
	a Scopetronix flexi-focus, and when I detached it to look at the focus
	pin that sticks out of the ETX, the pin actually withdrew into the
	housing of the telescope. So, now I'm in a real mess and I would
	appreciate advice as to how to proceed. I am pretty handy mechanically
	and would be comfortable attempting to fix it myself, but your advice on
	Mike's web page suggests that this isn't a home project.
	Any advice you can provide would be most helpful.
	Keith Egger
	Prince George, BC

Return to the top of this page.

Go back to the Tech Tips page.

Go back to the ETX Home Page.

Copyright ©1998-2000, 2004 Michael L. Weasner / etx@me.com
Submittal Copyright © 2000, 2004 by the Submitter
URL = http://www.weasner.com/etx/techtips/focusfix.html